X pipe or no X pipe? Exhaust question

[ENDEE666]

Already have an exhaust with an X pipe that I love from a sound standpoint. Some have said I should not have an X pipe cause it increases back pressure on turbo cars. Its located where the main cats used to be. Should I ditch it in favor of just pipes? Dual 2.5" btw. I noticed all of the S4 exhausts just have dual pipes with no X or H pipe..

[wofman]

I asked same question when considering custom, Nick (ended up with used Milltek, by the way -- perfect fit-up, no install concerns, but maybe a bit quieter than you'd like). Concluded that x is not helpful with turbos. Apparently some sound wave cancellation can occur to quiet sound a tad, but by definition, it impedes flow already created by turbos. Helps balance evacuation with naturally aspirated, but turbos already have exhaust spinning and direct path is best. Notice that no engineered systems include one and it's not like those manufacturers never heard of h-pipes or x-pipes. And it has nothing to do with cost of making the things (they're very cheap in these times). Probably doesn't hurt much, but does not help (except maybe some support for making pipes stay in place).

w

[Daft]

In an ideal case for peak power you would want both exhaust paths to be completely separate.

You really won't have any benefit from creating a location for gases to collide and slow down. The primary function you need is consistent exhaust gas velocity. The faster the gasses leave the pipe, the easier it is on the motor to perform its combustion process.

Since you have turbos, the turbine wheels will cause exhuast gasses to leave the combustion chamber but, once they are out, they need to travel quickly and smoothly as they cool and slow down.

Have you ever run the car with no cat back? It's got alot of extra power. Why? Because the exhaust gasses create no resistance on the turbine wheel and the turbine can turn much easier (less lag and more top end flow).

If I were building a high performance exhaust system, I'd make sure it met the following criteria:

1. Large enough inner diameter to flow the level of gasses I will be passing through it.
2. Least amount of bends possible and mandrel bent to promote less resistance.
3. No X-pipes or X-resonators to keep velocity at maximum levels.
4. Low resistance mufflers to not slow gasses at the exit point. Resonator type not baffle type.


This will not result in a quiet exhaust setup but, it will make the most power without running open pipe.

As another option, you could install dump pipes that open only under WOT and have a switchable max-power option. Dumps are cool but, very loud as they are essentially open downpipes under WOT.

[FrankA6]

Daft, i was just going to say the same thing....LOL

[doobiesdaddy]

No x pipe + No resonator + No cats + No mufflers = happy turbos

[ENDEE666]

Well all the answers were pretty much what I expected. I was just told the X would add some burble to the sound, but it doesn't seem it.

As of now, I have piggies, no main cats and all my mufflers are straight through and dual 2.5" with minimal bends and the X pipe where the main cats used to be. Surprisingly my exhaust is VERY quiet. Cruising at any speed (70 or even 140+) is amazingly silent inside. Hard accelleration definitely screams but in a super-car like way.. Only thing I would like to add would be a little of that VR6-like burble that the S4 seems to make. I think the X is what is robbing me of that..

And Daft, I was thinking about going with electric cutouts already. I may kill 2 birds with one stone and have those welded in where the X is. Then have a button inside to open them at the track or when racing.

Verdict is in. Thanks gents. The X must go....

[wofman]

So Daft, what causes the "burble" sound? I presume it has to do with back pressure or lack of it? I hear it with no throttle at low engne rpms, and of course you always get it on bikes going down hill, etc.

[PMAZ7]

So Daft, what causes the "burble" sound? I presume it has to do with back pressure or lack of it? I hear it with no throttle at low engne rpms, and of course you always get it on bikes going down hill, etc.

I know it can get annoying, but I dig that sound!

[ENDEE666]

Actually thats not the burble I mean. That I get a little and it will come from removing the cats mostly. I mean the sound a VR6 or S4 gets ON throttle like this-

http://www.youtube.com/watch?v=OhNIeZ7FzwU

http://www.youtube.com/watch?v=B_Wo1...eature=related

Kievsky's car, under boost
http://www.youtube.com/watch?v=PfAxl9Z6XZ0

The VR6 sound
http://www.youtube.com/watch?v=-sTmiwBl2kU

[twinsnailsS4]

^^^^Whoa...I want to know more about the 11 second run and congrats and what seems to be title of fastest A6.

http://www.s4biturbo.com/timeslips.php

[ENDEE666]

^^^^Whoa...I want to know more about the 11 second run and congrats and what seems to be title of fastest A6.

http://www.s4biturbo.com/timeslips.php

Thanks! I believe it is. I think I got that title after my first track run with a 12.3 cause the fastest I have seen record of was mid-upper 12's. I am waiting for my friend to edit the videos and I will likely be posting them along with the time slip. Not bad for a 2 ton quiet pig huh?

[twinsnailsS4]

^^^^Not too shabby at all I'll await a full thread on the runs with vids before I start asking more questions. Congrats again.

[Pearl_2.7T]

Everyone excuse my ignorance, but can someone explain "open dumps" to me? I understand the basics, but how are they controlled by a switch? Does anyone on here have them? If so, do you maybe have a clip of how loud they are? Lastly, are these expensive to have installed?

Thanks a bunch.

- Jared

[audirs]

i believe the electronic ones are activated by a switch, when you hit the switch it activates a solenoid that opens the closed pipe. i think i seen a site that has them for 425 bucks for 2, and installation wouldnt be too hard. probably a hundred or so bucks at a local exhaust shop. it would be insanely loud. if you drove around on open dumps ud get pulled over for sure, they are crazy loud.

ill try to dig up the site

[audirs]

http://shop.quicktimeperformance.com...oduct_list&c=4

depending on your pipe size will reflect price

[Pearl_2.7T]

i believe the electronic ones are activated by a switch, when you hit the switch it activates a solenoid that opens the closed pipe. i think i seen a site that has them for 425 bucks for 2, and installation wouldnt be too hard. probably a hundred or so bucks at a local exhaust shop. it would be insanely loud. if you drove around on open dumps ud get pulled over for sure, they are crazy loud.

ill try to dig up the site

Okay, performance wise would these result in anything additional? Or are you basically paying $425 for a crazy loud setup?

Edit: Also, aren't most downpipes a 2.5" cut-out, they have 2.25" and 3"?

- Jared

[ENDEE666]

Yeah, I have heard open dumps on a stage 3 S4 and they are super loud. The type of thing reserved for racing. But they free up a lot of power on turbo cars as well as help spool times.. I'm probably replacing my X with them..

[ENDEE666]

Okay, performance wise would these result in anything additional? Or are you basically paying $425 for a crazy loud setup?

Edit: Also, aren't most downpipes a 2.5" cut-out, they have 2.25" and 3"?

- Jared

Quote from QTP's page-
"30HP gain on a WRX
13HP on a LS1 Trans Am
20HP on a SRT4 Neon
75HP gain on a Turbo Honda
3 Tenths gain at the track for a VW 1.8T Jetta
35HP gain on Ford Lightning Truck"

As you can see, forced induction cars get nice improvements from them. And knowing someone with them, I can tell you he agrees as well.. How much of a gain depends on setup and how restrictive your exhaust is. I would also assume a Stage 3 car running 23 psi with K04s would see more than a chipped car running 14 psi with K03s.. And a GT28 car would see even more.. Another variable is if you have cats in your exhaust and run dumps before them you will see HUGE gains.. When I took the cats out of my car (piggies for pre cats, no main cats) I saw some serious gains...

[Pearl_2.7T]

Quote from QTP's page-
"30HP gain on a WRX
13HP on a LS1 Trans Am
20HP on a SRT4 Neon
75HP gain on a Turbo Honda
3 Tenths gain at the track for a VW 1.8T Jetta
35HP gain on Ford Lightning Truck"

As you can see, forced induction cars get nice improvements from them. And knowing someone with them, I can tell you he agrees as well.. How much of a gain depends on setup and how restrictive your exhaust is. I would also assume a Stage 3 car running 23 psi with K04s would see more than a chipped car running 14 psi with K03s.. And a GT28 car would see even more.. Another variable is if you have cats in your exhaust and run dumps before them you will see HUGE gains.. When I took the cats out of my car (piggies for pre cats, no main cats) I saw some serious gains...

Thanks for all of the information. I guess the good thing about electronic dumps is that you don't always have to have them open, correct? You can open and close as you please. Is $425 a fair price in your opinion? Or do you think others may offer them at a better price?

Edit: I did some research and many folks stated that DMH has quality electric cutouts...

http://www.dmhperformance.com/ecutout.htm

- Jared

[ENDEE666]

I have seen them anywhere from $175-220 each. So thats average. And yes, the point is that they are only open when the switch is activated.

[Pearl_2.7T]

I have seen them anywhere from $175-220 each. So thats average. And yes, the point is that they are only open when the switch is activated.

Thanks again for all your help. Also, congrats on getting into the 11's, that's a great accomplishment. I'm lucky to get into the 13's ha-ha

[easymacgyver]

The RS6 exhaust has no X-pipe - it is set up to be able to do it, but the factory didn't. They did X the stock 4.2 however.
So I'd say, turbo cars, no X, NA cars yes X.
I X'd my RS6 pipes for my NA 4.2 and it works well.

[RS6-4dr911]

I have no hard data to back it up, but it was my understanding that the purpose of an x-pipe was to allow 1 bank of cylinders to use both exhaust pipes. Since the banks are out of phase, the pulses arrive at the "x" in an alternating fashion regardless of rpm, so the exhaust thinks it has half the back pressure. Doing this, by the way, is good for increased power but often hurts low end torque.

The reason that an x-pipe has little or no effect on a turbo car is because the turbine blades smooth the exhaust from pulses to a smooth flow, so there is not an opportunity for the flow to be smoothed out any(much) further, hence, no gain and why the factory doesn't bother.

Be careful about looking to the factory for what works and what doesn't. Their corporate goals and constraints are often not clear to anyone other than an industry insider, and these often run counter to maximum horsepower or other desireable traits for enthusiasts. That's why chips often create small peak power gains but huge gains in mid-range power and driveability. Government compliance goals call for good CAFE mileage numbers, marketing goals call for good-lookin-on-paper HP numbers and 0-60 times. That leaves the mid-range as a place where they can manipulate fuel and timing curves to achieve both but driveability suffers. Enter the tuners.

[sempaipaul]

Actually thats not the burble I mean. That I get a little and it will come from removing the cats mostly. I mean the sound a VR6 or S4 gets ON throttle like this-

http://www.youtube.com/watch?v=OhNIeZ7FzwU

http://www.youtube.com/watch?v=B_Wo1...eature=related

Kievsky's car, under boost
http://www.youtube.com/watch?v=PfAxl9Z6XZ0

The VR6 sound
http://www.youtube.com/watch?v=-sTmiwBl2kU

Yeah I love the way kievsky's a6 sounds and I was actually considering putting on an x pipe on my magnaflow system.... But now you guys are saying it's bad for our turbo cars?

[wofman]

RS6/911 --I'm a tad leary of notion that Audi's corporate goals are so mysterious or that factory tries to limit desirable traits. Certainly there's no "mileage" in omission of simple, cheap way to improve anything, and having no x-pipe certainly has nothing to do with CAFE mileage or "on paper" anything. Check with GIAC or APR about your chip data. I'm not an engineer, will defer to Daft and Sam.

Daft, my mechanic and what I've gleaned when I was considering custom set up using these all point to same issues: turbos send out spiraling exhaust gases, uninterrupted flow is better than collisions. Straight back is better. Noise cancellation occurs with x-pipes (sound waves filling each others' troughs) but I assume less sound loss than with resonators. And some extra gas evacuation improvements can occur with naturally aspirated engines that use x-pipes, not turbos.

And if you have an RS6 and 911 then I'm unabashedly jealous!

[ENDEE666]

Yeah I love the way kievsky's a6 sounds and I was actually considering putting on an x pipe on my magnaflow system.... But now you guys are saying it's bad for our turbo cars?

Thats what made me do one... Then I realized that my friends with S4's and true dual setups have no X and sound more like his than I do. That VR6 full throttle burble is what I want...

[doobiesdaddy]

Thats what made me do one... Then I realized that my friends with S4's and true dual setups have no X and sound more like his than I do. That VR6 full throttle burble is what I want...

If this is the sound you want get rid if your mufflers and resonators. Turbo back straight pipe is the way to go if you want that burble sound.

[ENDEE666]

If this is the sound you want get rid if your mufflers and resonators. Turbo back straight pipe is the way to go if you want that burble sound.

Just to be clear, since some mix up the sound I mean, I mean the 'gargle' type of sound ON throttle, not the burble off throttle of an open exhaust...

Decided the X is gonna go. Hopefully take care of it tomorrow...

[doobiesdaddy]

Let us know how it turns out!
need sound clips!

[2.slowT]

How did this turn out?

I am in the process of selecting a setup now.

Piggies (leaving main cats), removing resignator, & magnaflow mufflers is what I have come up with so far.

What I dont know is to remove main cats also, add x (for sound), or use come 4/6" cans to reduce noise.

[ENDEE666]

I ended up replying on another exhaust thread about the results. I took the X off and a half hour later went right back and put it back on. I didn't notice much of a power change, a loss in mid range if anything at all. But the sound ended up awful without it. It reminded me of like a Mustang V6 or Camaro V6 with exhaust. Simply awful... Now its back on & I love it anyway. Quiet when cruising, screams like a supercar under boost.. Perfect.

[2.slowT]

I ended up replying on another exhaust thread about the results. I took the X off and a half hour later went right back and put it back on. I didn't notice much of a power change, a loss in mid range if anything at all. But the sound ended up awful without it. It reminded me of like a Mustang V6 or Camaro V6 with exhaust. Simply awful... Now its back on & I love it anyway. Quiet when cruising, screams like a supercar under boost.. Perfect.

You should definately visit this thread I just created and post your specs and experiance.

[wofman]

you should use free-flow cats, not stock

[ENDEE666]

Or no cats at all like me